Alternator for vehicle

ABSTRACT

An alternator has a rectifier converting an alternating current to a direct current. The rectifier has a heat sink and rectifying elements. The sink has front and rear surfaces opposite to each other along a depth direction. The sink has holes each extending along the depth direction. Each element has a disk disposed in one hole and a semiconductor pellet attached to the disk. Each disk has upper and bottom surfaces opposite to each other along the depth direction. Each pellet is disposed on the upper surface. A contact surface of each disk is in contact with the sink. A position of the upper surface of each disk is placed between the first and second surfaces of the heat sink. A range of the contact surface of each disk is within a range between the upper and bottom surfaces of the disk.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application 2006-231708 filed on Aug. 29, 2006 sothat the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an alternator mounted on avehicle such as a passenger car, a truck or the like, and moreparticularly to an alternator with a rectifier for rectifying analternating current generated in the alternator.

2. Description of Related Art

A slant nose type vehicle has recently been required to decrease arunning resistance in a vehicle and to improve a field of vision for adriver. Further, a wide accommodation space of a vehicle compartment hasrecently been required to give better comfort to occupants of thevehicle. These requirements narrow an engine room space. In addition,the number of members disposed around an engine of the vehicle has beenincreased. Therefore, an alternator is inevitably disposed near theengine, so that heat received in the alternator from the engine has beenincreased. Further, the alternator is required to be made in a smallersize.

Further, because the number of current consumers has been increased toimprove comfort and safety to the occupants, the alternator is requiredto generate a larger electrical energy. Therefore, heat generated in thealternator itself has been increased. Particularly, a rectifier havingmany diodes generates a large amount of heat. Therefore, it is requiredto improve a cooling performance of the rectifier disposed in a narrowspace at a low cost. Each diode of the rectifier has a semiconductorpellet and a disk electrically connected with each other. To dissipateheat generated in the semiconductor pellets to the atmosphere, the disksof the rectifier are attached to a heat sink by soldering.

Further, to prevent thermal fatigue caused in the solder during the diskattachment, Published Japanese Patent First Publication No. 2002-119029discloses an alternator wherein disks of rectifying elements (or diodes)of a rectifier are pressed into holes opened in a heat sink to fix therectifying elements to the heat sink. In this alternator, the disks areformed of a material having a hardness higher than that of the heatsink. Therefore, the disks are hardly deformed when being inserted intothe holes, and stresses of the disks on semiconductor pellets arereduced. Further, in this rectifier, the thickness of each disk is setto be equal to or larger than that of the heat sink to place thesemiconductor pellet away from a side surface of the disk being incontact with the heat sink. With this structure, when the disk ispressed into a hole of the heat sink, a compressive stress added to thesemiconductor pellet is considerably reduced.

However, holes in the heat sink are formed by the deformation processingsuch as press processing. In this case, a size of each hole cannot beprecisely set, so that an allowance between the hole and disk becomesinsufficient. Further, hardness at portions of the heat sink surroundingthe holes is heightened by the deformation processing, so that it isdifficult to sufficiently reduce stress on the semiconductor pellet whenthe disk is pressed into the hole. Further, when the disk is thickenedso as to place the semiconductor pellet further away from a surface ofthe disk being contact with the heat sink, each rectifying elementbecomes large in a thickness direction. Therefore, the rectifier cannotbe downsized.

Further, Published Japanese Patent First Publication No. 2004-112860discloses an alternator wherein a plurality of sub-fins are formed in acomplicate structure by deforming an aluminum plate by die casting andare attached to a heat sink to stand on the heat sink. Therefore, a heatdissipating area of the heat sink becomes large, so that a coolingperformance of the rectifier can be improved without enlarging the heatsink along its extending direction.

However, although the sub-fins deformed by die casting can bearbitrarily shaped to heighten the cooling performance of the rectifier,surface portions of the sub-fins are hardened due to the casting. Inthis case, when the disks are pressed into the holes of the heat sink,it is sometimes difficult to reduce a stress on the semiconductorpellets.

SUMMARY OF THE INVENTION

An object of the present invention is to provide, with due considerationto the drawbacks of the conventional alternator, an alternator wherein astress of a disk on a semiconductor pellet in a rectifying element of arectifier is reduced regardless of hardness of a heat sink of therectifier and hardness of the disk.

According to an aspect of this invention, the object is achieved by theprovision of an alternator with a rectifier, the rectifier comprising aheat sink having a plurality of holes, and a plurality of rectifyingelements, respectively, having a plurality of disks disposed in theholes of the heat sink and a plurality of semiconductor pellets attachedto the disks. The heat sink has a first surface and a second surfaceopposite to each other along a depth direction of the rectifier. Eachhole extends from the first surface along the depth direction. Thesemiconductor pellets are electrically connected with one another so asto produce a direct current from an alternating current. Each disk hasan upper surface and a bottom surface opposite to each other along thedepth direction. Each semiconductor pellet is disposed on the uppersurface of the corresponding disk. A contact of each disk with the heatsink is limited to a contact surface of the disk. A position of theupper surface of each disk in the depth direction is set to place theupper surface between the first and second surfaces of the heat sink. Arange of the contact surface of each disk in the depth direction is setto be within a range from the bottom surface of the disk to the uppersurface of the disk.

With this structure, the alternator has the first feature that aposition of the upper surface of each disk in the depth direction isplaced between the first and second surfaces of the heat sink.Accordingly, as compared with a case where the thickness of a disk isequal to or larger than that of a heat sink according to a prior art,the length of each rectifying element can be shortened in the depthdirection.

Further, the alternator has the second feature that a range of thecontact surface of each disk in the depth direction is within a rangefrom the bottom surface to the upper surface of the disk. The diskreceives a pushing force from the heat sink through the contact surfacealong directions perpendicular to the depth direction when being pressedinto one hole of the heat sink or being forcibly fitted to the heatsink. However, the semiconductor pellet disposed on the upper surface ofthe disk hardly receives this pushing force from the heat sink throughthe disk. Accordingly, a stress on the semiconductor pellet can bereduced regardless of hardness of the heat sink and hardness of thedisk, so that the attachment of the semiconductor pellet to the disk canbe stably maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of an alternator according to anembodiment of the present invention;

FIG. 2 is an electric circuit diagram of a rectifier shown in FIG. 1;

FIG. 3 is a plan view of the rectifier seen from the rear side;

FIG. 4 is a sectional view of a rectifying element attached to a heatsink shown in FIG. 1;

FIG. 5 is a sectional view of a rectifying element attached to a heatsink according to a second modification of the embodiment;

FIG. 6 is a sectional view of a rectifying element attached to a heatsink according to a third modification of the embodiment; and

FIG. 7 is a sectional view of a rectifying element attached to a heatsink according to a fourth modification of the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment and its modifications of the present invention will now bedescribed with reference to the accompanying drawings, in which likereference numerals indicate like parts, members or elements throughoutthe specification unless otherwise indicated.

Embodiment 1

FIG. 1 is a longitudinal sectional view of an alternator used for avehicle according to this embodiment. As shown in FIG. 1, an alternator1 has a cylindrical stator 2, a columnar rotor 3 disposed in a centerhole of the stator 2, a brush device 4, a rectifier 5, a regulator 12, aframe 6, a pulley 8 fixed to the rotor 3 on a front side of thealternator 1, and a rear cover 7.

The stator 2 has a stator core 21, a three-phase stator wiring 23 and aninsulator 24 electrically insulating the wiring 23 from the core 22. Thecore 21 has a plurality of slots aligned at equal intervals along acircumferential direction of the stator 2. The wiring 23 areaccommodated in each of the slots to be wound around the core 22. Thewiring 23 has three phase wirings connected with one another inY-connection.

The rotor 3 has a rotational shaft 33, a pair of pole cores 32 fixed tothe shaft 33 so as to place the shaft 33 in a center hole of the core32, and a field wiring 31 wound around the core 32 cylindrically andcoaxially. The cores 32 have a plurality of nail portions aligned alonga circumferential direction of the core 32. The wiring 31 is formed of acopper wire covered with insulator or resin. A cooling fan 34 isattached, by welding or the like, to a front end surface of one polecore 32 placed on the front side. A cooling fan 35 is attached, bywelding or the like, to a rear end surface of the other pole core 32placed on a rear side of the alternator 1.

Two slip rings 36 and 37 are attached to a rear portion of the shaft 33so as to be rotated with the shaft 33. Each of the slip rings 36 and 37has two half portions, respectively, connected with ends of the wiring31 through conductor lines 38 and 39.

The brush device 4, the rectifier 5 and the regulator 12 are fixed to arear portion of the frame 6 and are covered with the rear cover 7 on therear side.

The brush device 4 has two brushes 41 and 42, respectively, pressing therings 36 and 37. A field current is supplied from the rectifier 5 to thewiring 31 of the rotor 3 through the brush device 4 and the rings 36 and37. A flow direction of the field current in the wiring 31 is changedevery half rotation of the shaft 33, so that a three-phase alternatingcurrent is generated in the stator wiring 23.

The rectifier 5 rectifies the alternating current of the wiring 23 toproduce a direct current as an electrical energy generated in thealternator 1. The rectifier 5 has a terminal board 51 in whichconnection terminals are embedded, a positive electrode side heat sink52 and a negative electrode side heat sink 53 facing each other at apredetermined interval, six rectifying elements (or diodes) 54 fitted tothe heat sink 52, and six rectifying elements (or diodes) 55 fitted tothe heat sink 53. The rectifying elements 54 and 55 serve assemiconductor devices. Heat generated in the elements 54 and 55 aretransmitted to the heat sinks 52 and 53 and is dissipated to theatmosphere.

Further, the elements 54 and 55 are connected with the connectionterminals of the board 51 so as to form a diode bridge circuit. Theelements 54 are electrically connected with the heat sink 52, and theheat sink 52 is electrically connected with a positive electrode of abattery (not shown). The elements 55 are electrically connected with theheat sink 53, and the heat sink 53 is earthed. FIG. 2 is an electriccircuit diagram of the rectifier 5. As shown in FIG. 2, each of therectifying elements 54 and 55 is formed of a diode, and the rectifier 5has two diode bridge circuits arranged in parallel to each other.

The regulator 12 regulates a value of the field current supplied to thefield coil 31 to control an electrical energy generated in thealternator 1.

The frame 6 accommodates the stator 2 and the rotor 3. The frame 6 has afront bearing 63 and a rear bearing 64. The bearing 63 rotatably holdsthe front portion of the shaft 33. The bearing 64 rotatably holds therear portion of the shaft 33. The frame 6 holds the stator 2 and therotor 3 such that the rotor 3 is disposed in a center hole of the stator2 at a predetermined interval from the stator 2. The frame 6 further hasa plurality of outlet windows 61 and inlet windows 62. The windows 61are aligned along the circumferential direction so as to face an endportion of the wiring 23 protruded from the core 21 toward the frontside. The windows 62 are opened on the front and rear sides,respectively. When the fans 34 and 35 are rotated with the cores 32 andthe shaft 33, the fans 34 and 35 receive cooling winds through the inletwindows 62, cools the stator 2 and the rotor 3 and discharge the windsthrough the outlet windows 61.

With this structure of the alternator 1, when a rotational force istransmitted from an engine (not shown) of a vehicle to the shaft 33through a belt (not shown) and the pulley 8, the rotor 3 is rotated along a predetermined rotation direction. When a field current issupplied from the rectifier 5 to the field wiring 31 of the rotatedrotor 3 through the brush device 4, the nail portions of the rotatedcores 32 are magnetized. Therefore, a three-phase alternating current isgenerated in the stator wiring 23. The regulator 12 adjusts the fieldcurrent on the basis of a voltage of a battery (not shown) to controlthe current of the wiring 23. The rectifier 5 converts the alternatingcurrent of the wiring 23 into a direct current. This direct current isoutputted to current consumers and the battery. Further, the directcurrent is supplied to the regulator 12 as the field current.

Next, a structure of the rectifier 5 is described in detail withreference to FIG. 3 and FIG. 4.

FIG. 3 is a plan view of the rectifier 5 seen from the rear side. Asshown in FIG. 3, the heat sink 52 has six holes almost concentricallydisposed, and the rectifying elements 54 are, respectively, pressed intothe holes of the heat sink 52 so as to be attached to the heat sink 52.The heat sink 53 has six holes 56 almost concentrically disposed, andthe rectifying elements 55 are, respectively, pressed into the holes 56of the heat sink 53 so as to be attached to the heat sink 53. Becausethe elements 54 and 55 are attached to the heat sinks 52 and 53 withoutusing solder, the elements 54 and 55 can be attached to the heat sinks52 and 53 at a lower cost while reducing the number of working steps forattaching the elements 54 and 55 to the heat sinks 52 and 53.

FIG. 4 is a sectional view of one rectifying element 55 attached to theheat sink 53. All the elements 55 are attached to the heat sink 53 inthe same manner as the element 55 shown in FIG. 4. Further, therectifying elements 54 are attached to the heat sink 52 in the samemanner as the elements 55 attached to the heat sink 53., so thatdetailed descriptions and illustrations for the elements 54 attached tothe heat sink 52 are omitted.

As shown in FIG. 4, the heat sink 53 has a front surface 531 and a rearsurface 532 opposite to each other along a depth direction of therectifier 5. Each rectifying element 55 has a semiconductor pellet 510and a disk 500 disposed in the hole of the heat sink 53. The pellets 510of the elements 55 are electrically connected with one another so as toproduce the direct current from the alternating current. The disk 500 isformed in a columnar shape having a concavity 504 on its one end. Thedisk 500 has an upper surface 506 and a bottom surface 501 opposite toeach other along the depth direction. The upper surface 506 denotes abottom of the concavity 504. A material of the disk 500 preferably has ahardness higher than that of a material of the heat sink 53. However, amaterial of the disk 500 may have a hardness equal to or lower than thatof a material of the heat sink 53.

The semiconductor pellet 510 is soldered to the disk 500 on the uppersurface 506, so that the pellet 510 is disposed on the upper surface 506through a solder layer 512. Further, a lead line 520 is soldered to thepellet 510, so that the lead line 520 is disposed on the pellet 510through another solder layer 514. The pellet 510 is covered with aprotective layer 522 made of silicon rubber or resin.

More specifically, the disk 500 has both a solid portion 500 a placedbetween the surfaces 501 and 506 and a hollow portion 500 b having theconcavity 504. Stiffness of the solid portion 500 a in directionsperpendicular to the depth direction is higher than that of the hollowportion 500 b. A side wall of the heat sink 53 facing its hole is formedin a stepped shape so as to have an opening 530 between at least thehollow portion 500 b of the disk 500 and the heat sink 53. The solidportion 500 a is pressed into the hole of the heat sink 53 along adirection from the front surface 531 to the rear surface 532 such that apress fitting surface (or contact surface) 502 of the disk 500 isdirectly in contact with the heat sink 53. The hollow portion 500 b andthe heat sink 53 face each other with the opening 530 between, so thatthe hollow portion 500 b is disposed away from the heat sink 53.Therefore, the solid portion 500 a receives a pushing force from theheat sink 53 along directions substantially perpendicular to the depthdirection, so that the disk 500 is forcibly fitted to the heat sink 53.In contrast, the hollow portion 500 b receives no pushing force from theheat sink 53.

A position of the upper surface 506 in the depth direction is set toplace the upper surface 506 at a level between the surfaces 531 and 532of the heat sink 53. That is, the upper surface 506 is placed within thehole of the heat sink 53 so as to shorten a length of the element 55 inthe depth direction.

Further, a range of the press fitting surface 502 of the disk 500 in thedepth direction is set to be within a range from the bottom surface 501to the upper surface 506 of the disk 500. In this embodiment, forexample, the bottom surface 501 of the disk 500 and the rear surface 532of the heat sink 53 are placed on the same plane, and a length of thesurface 502 in the depth direction is set to be shorter than a distancebetween the surfaces 501 and 506.

Assuming that all portions of a disk including a hollow portion arepressed into a hole of a heat sink such that the hollow portion is incontact with the heat sink, the hollow portion receives a pushing forcefrom the heat sink and is deformed. In this case, both a semiconductorpellet and a solder layer between the pellet and the disk are deformedin a conical shape. Therefore, the pellet is broken, or/and the pelletis detached from the disk.

In contrast, in this embodiment, only the solid portion 500 a of thedisk 500 having a higher stiffness is pressed into the hole of the heatsink 53. Therefore, the hollow portion 500 b receives no pushing forcefrom the heat sink when being inserted into the hole and being placed inthe hole after the insertion. In this case, the hollow portion 500 b isnot substantially deformed, so that a stress on the pellet 510 and thesolder layer 512 surrounded by the hollow portion 500 b can beconsiderably reduced.

Accordingly, a stress on the pellet 510 of each rectifying element inthe rectifier 5 can be reduced regardless of hardness of the heat sinks52 and 53 and hardness of the disk 500 of each rectifying element. Thatis, the connection of the pellet 510 with the disk 500 can be stablymaintained.

Modification 1

The heat sink 53 is formed by casting or deformation processing, so thata surface portion of the heat sink 53 surrounding each hole is hardened.Assuming that the contact surface 502 of the disk 500 is forcibly incontact with the hardened surface portion of the heat sink 53, it isrequired to further heighten a hardness of the disk 500 for the purposeof suppressing the deformation of the disk 500.

In this modification, the hardened surface portion of the heat sink 53is preferably cut by a machine work, so that a contact portion of theheat sink 53 not hardened is forcibly in contact with the press fittingsurface 502 of the disk 500. In this case, the hardness of the disk 500can be set to be slightly higher than the hardness of the heat sink 53.Accordingly, a cost for producing the disk 500 can be lowered whilesuppressing the deformation of the disk 500 forcibly fitted to the heatsink 53. That is, a stress on the pellet 510 can be further reduced.

Modification 2

FIG. 5 is a sectional view of one rectifying element 55 attached to theheat sink 53 according to a second modification of this embodiment.

As shown in FIG. 5, a circumferential side surface of the disk 500facing the heat sink 53 is formed in a stepped shape so as to have anopening 534 between at least the hollow portion 500 b of the disk 500and the heat sink 53. The press fitting surface 502 of the disk 500corresponds to a portion of the circumferential side surface of the disk500 facing no opening. A side surface of the heat sink 53 surroundingits hole is formed in a flat shape along the depth direction.

Because the hollow portion 500 b of the disk 500 and the heat sink 53face each other with the opening 534 between, the hollow portion 500 bis not in contact with the heat sink 53. Therefore, the hollow portion500 b of the disk 500 fitted to the heat sink 53 receives no stress fromthe heat sink 53. Accordingly, in the same manner as in the rectifyingelement 55 shown in FIG. 4, a stress on the pellet 510 of the rectifyingelement 55 in the rectifier 5 can be reduced.

Further, when the disk 500 is pressed into the hole of the heat sink 53along a fitting direction (or upper direction in FIG. 5) from the rearsurface 532 to the front surface 531, the hollow portion 500 b of thedisk 500 does not come in contact with the heat sink 53. Accordingly,even when the disk 500 is pressed into the hole of the heat sink 53along the fitting direction, a stress on the pellet 510 can be reduced.That is, the connection of the pellet 510 with the disk 500 can bestably maintained.

Modification 3

FIG. 6 is a sectional view of one rectifying element attached to theheat sink 53 according to a third modification of this embodiment.

As shown in FIG. 6, a disk 500A of each rectifying element 55A of therectifier 5 differs from the disk 500 shown in FIG. 4 in that the disk500A has a knurling portion 540 facing a side wall of the heat sink 53.The knurling portion 540 is formed by processing an outer surfaceportion of the disk 500A by knurling. A surface of the knurling portion540 is composed of both a press fitting surface (or contact surface) 502being in contact with the heat sink 53 and a non-contact surfacedisposed away from the heat sink 53 through the opening 530.

When the disk 500 shown in FIG. 4 is pressed into a hole of the heatsink 53 at a press-fitting force, a stress on the pellet 510 and thesolder layer 512 is changed in proportional to the press-fitting force.Further, in a case where a size of the disk 500 is larger than thatappropriate to a size of the hole, it is required to press the disk 500into the hole at a larger press-fitting force. Therefore, when the disk500 not processed by knurling is pressed into a hole of the heat sink53, it is required to determine a size of the disk 500 with highprecision.

In contrast, in this modification, even when a size of the disk 500Ahaving the knurling portion 540 is not precisely determined, the disk500A can be pressed into a hole of the heat sink 53 at a properpress-fitting force. Accordingly, a stress on the pellet 510 can befurther reduced, and the connection of the pellet 510 with the disk 500can be stably maintained.

In this modification, the whole side portion of the disk 500A facing theheat sink 53 is processed by knurling. Therefore, the knurling can beeasily performed without predetermining an area for the knurling portion540 with high precision. However, only a limited side portion of thedisk 500A, on which the press-fitting portion 502 is formed, may beprocessed by knurling.

Further, the disk 500A may have a stepped wall facing the heat sink 53such that the press-fitting surface 502 is formed on a knurling portionof the disk 500A.

Modification 4

FIG. 7 is a sectional view of one rectifying element 55 attached to theheat sink 53 according to a fourth modification of this embodiment.

As shown in FIG. 7, the opening 534 is packed with a predeterminedmaterial 550. As compared with materials of the disk 500 and the heatsink 53, the material 550 has a low elasticity, and a thermalconductivity of the material 550 is not so low or is substantially thesame as a thermal conductivity of the disk 500 or the heat sink 53.

Therefore, even when the alternator 1 receives water or liquid with anantifreezing agent spread on a road, there is no probability that thewater or liquid enters the opening 534. Accordingly, various problemssuch as corrosion caused in the rectifier 5 by the water or liquid canbe prevented.

Further, even when the material of the disk 500 differs from that of theheat sink 53 so as to produce a difference in coefficient of linearthermal expansion between the disk 500 and the heat sink 53, stress onthe disk 500 caused by a change in temperature can be absorbed by thematerial 550 having a low elasticity. Accordingly, a stress on thepellet 510 can be reduced, and the connection of the pellet 510 with thedisk 500 can be stably maintained.

Moreover, because the material 550 has a preferable thermalconductivity, heat generated in the pellet 510 can be smoothlytransmitted to the heat sink 53 through the material 550. Accordingly, acooling performance of the rectifier 5 can be improved.

In this modification, only the opening 534 is packed with the material550. However, all the rectifier 5 including the opening 534 may becovered with a paint film having a low elasticity to prevent variousproblems caused by water or liquid including an antifreezing agent.

Further, in the same manner as the opening 534 packed with the material550, the opening 530 shown in FIG. 4 or FIG. 6 may be packed with thematerial 550.

In the embodiment and modifications, each of the holes in the heat sinks52 and 53 penetrates through the corresponding heat sink. However, eachof the heat sinks 52 and 53 may have a thinned-wall portion on whicheach of non-penetrating holes is placed. In this case, each disk 500 maybe attached to one thinned-wall portion by a conductive adhesivematerial such as solder.

Further, although the rectifier 5 is disposed in the alternator 1, thisembodiment should not be construed as limiting the present invention.For example, the present invention can be applied for any semiconductordevice including the rectifier 5.

1. An alternator, which generates an alternating current, converts thealternating current to a direct current in a rectifier and outputs thedirect current, the rectifier comprising: a heat sink having a pluralityof holes, the heat sink having a first surface and a second surfaceopposite to each other along a depth direction of the rectifier, each ofthe holes extending from the first surface along the depth direction;and a plurality of rectifying elements, respectively, having a pluralityof disks disposed in the holes of the heat sink and a plurality ofsemiconductor pellets attached to the disks, the semiconductor pelletsbeing electrically connected with one another so as to produce thedirect current from the alternating current, each of the disks having anupper surface and a bottom surface opposite to each other along thedepth direction, each of the semiconductor pellets being disposed on theupper surface of the corresponding disk, a contact of each of the diskswith the heat sink being limited to a contact surface of the disk,wherein a position of the upper surface of each disk in the depthdirection is set to place the upper surface between the first and secondsurfaces of the heat sink, and a range of the contact surface of eachdisk in the depth direction is set to be within a range from the bottomsurface of the disk to the upper surface of the disk.
 2. The alternatoraccording to claim 1, wherein each of the disks has a knurling portionsuch that an outer circumferential surface of the disk facing the heatsink and including the contact surface is placed on the knurlingportion, the knurling portion being obtained by processing an outercircumferential portion of the disk by knurling.
 3. The alternatoraccording to claim 1, wherein each of the disks has a knurling portionon which the contact surface of the disk is placed, the knurling portionbeing obtained by processing the disk by knurling.
 4. The alternatoraccording to claim 1, wherein a contact portion of the heat sink beingin contact with the contact surface of the disk is obtained by cuttingoff an outer surface portion of the heat sink by a machine work.
 5. Thealternator according to claim 1, wherein the heat sink has a steppedwall surrounding each hole so as to have an opening between thecorresponding disk and the heat sink, and the disk has a non-contactsurface spaced from the heat sink through the opening such that both thecontact surface and the non-contact surface of the disk serve as a sidesurface facing the heat sink.
 6. The alternator according to claim 1,wherein each disk has a stepped wall facing a side wall of thecorresponding hole of the heat sink so as to have an opening between thestepped wall of the disk and the side wall of the heat sink, and thestepped wall of the disk is partitioned into both the contact surfaceand a non-contact surface spaced from the heat sink through the opening.7. The alternator according to claim 1, wherein each disk has a sidesurface facing the heat sink, the side surface is divided into thecontact surface and a non-contact surface disposed away from the heatsink through an opening, and the opening is packed with a predeterminedmaterial differing from materials of the heat sink and the disk.
 8. Thealternator according to claim 7, wherein the predetermined material hasan elasticity lower than those of the heat sink and the disk.
 9. Thealternator according to claim 7, wherein the predetermined material hasa thermal conductivity substantially the same as that of the heat sinkor the disk.
 10. The alternator according to claim 1, wherein the rangeof the contact surface of each disk agrees with the range from thebottom surface of the disk to the upper surface of the disk.
 11. Thealternator according to claim 1, wherein each rectifying element ismounted on the upper surface through a solder layer.
 12. The alternatoraccording to claim 1, wherein each disk has a side wall disposed on itsupper surface so as to place the corresponding semiconductor pellet in aconcavity surrounded by the side wall.
 13. The alternator according toclaim 1, wherein the contact surface of each disk is in contact with theheat sink such that the disk is forcibly fitted to the heat sink. 14.The alternator according to claim 1, wherein each disk is adapted to bepressed into the heat sink to make the contact surface of the disk beingin contact with the heat sink.
 15. The alternator according to claim 1,wherein each hole of the heat sink penetrates through the heat sink fromthe first surface to the second surface of the heat sink.
 16. Thealternator according to claim 1, wherein the heat sink has a bottomportion such that each hole extends from the first surface to the bottomportion, and the bottom surface of the corresponding disk is disposed onthe bottom portion of heat sink.